This invention relates to the manufacture of 1,1'-dialkyl-4,4'-bipyridylium salts.
It is known that dialkylsulphates, for example dimethylsulphate, may be used as quaternising agents in the preparation of 4,4'-bipyridylium salts from 4,4'-bipyridyls. In the known reaction it is usual to employ at least the stoichiometric proportion of the dialkylsulphate for the formation of the alkylsulphate salt, for example in the formation of the dimethosulphate: ##STR1## from 4,4'-bipyridyl itself, at least 2 moles of dimethylsulphate are used per mole of 4,4'-bipyridyl.
The aforesaid reaction has the disadvantage that only up to half of the alkyl groups in the dialkylsulphate are utilised in the production of the 1,1'-dialkyl-4,4'-bipyridylium cation. Furthermore, dialkylsulphates are highly reactive reagents which are unpleasant, and potentially dangerous, to handle in the quaternisation process.